Add blogpost on FerretDB v1.4.0

[Fashander]

Description

Readiness checklist

• I added/updated unit tests.
• I added/updated integration/compatibility tests.
• I added/updated comments and checked rendering.
• I made spot refactorings.
• I updated user documentation.
• I ran task all, and it passed.
• I ensured that PR title is good enough for the changelog.
• (for maintainers only) I set Reviewers (@FerretDB/core), Labels, Project and project's Sprint fields.
• I marked all done items in this checklist.

[mergify]

Marketing blog posts should be reviewed by @ptrfarkas and @AlekSi.

[Fashander]

@AlekSi PTAL

[codecov]

Codecov Report

Merging #2858 (a92c175) into main (9a8085b) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2858   +/-   ##
=======================================
  Coverage   63.77%   63.77%           
=======================================
  Files         448      448           
  Lines       22890    22890           
=======================================
  Hits        14598    14598           
  Misses       7334     7334           
  Partials      958      958           

Flag	Coverage Δ
integration	56.84% <ø> (ø)
mongodb	4.26% <ø> (ø)
pg	56.75% <ø> (ø)
shard-1	43.53% <ø> (ø)
shard-2	41.23% <ø> (+0.01%)	⬆️
shard-3	42.55% <ø> (ø)
unit	24.80% <ø> (-0.03%)	⬇️

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